Apple, which has long perpetuated the belief that its operating system is immune to security problems, is recommending that users install security software to make it harder for hackers to target its platform.

“Apple encourages the widespread use of multiple antivirus utilities so that virus programmers have more than one application to circumvent, thus making the whole virus writing process more difficult,” according to a support note posted last month. The note was first spotted by The Washington Post.

Of course, this isn’t the first time Apple has told Mac users to protect themselves against viruses. The 9to5Mac blog points to warnings from 2002 and earlier this year that also dealt with virus protection.

Still, data by computer security researchers has shown that while Apple hasn’t been affected by malicious software nearly to the extent as Windows, it’s merely because hackers go after the most widely used platform.

Apple is gaining market share, however, which means hackers could increasingly look to exploit the platform, particularly if it becomes perceived as an easier target.

In the past, Apple has been slow to patch, according to researchers from the Swiss Federal Institute of Technology. They released a study in March looking at so-called zero-day vulnerabilities, when a security problem is publicly disclosed without a patch.

That measure is important since it means users are unprotected during the time it takes to create, test and then apply a patch. The study concluded Apple often had more unpatched vulnerabilties than Microsoft.

Apple systems are also not immune from problems in third-party software, such as plug-ins, which are used to view animated Flash graphics and PDF (Portable Document Format) files.

Security problems in plug-ins have frequently been manipulated to cause browsers to redirect to malicious Web sites, which are rigged to try and take advantage of browser flaws.

Compared to Windows, there aren’t nearly as many antivirus products for Apple computers. Russian security vendor Kaspersky Lab, however, said earlier this year that it has a prototype Apple version of its software that it could publish in days depending on market demand. Symantec, McAfee and Intego offer Apple antivirus products as well.

Sophos, based in Abingdon, England, currently sells an enterprise-level product for OS X, and interest has been increasing in the product, said Graham Cluley, senior technology consultant.

Analysts in the company’s labs have seen more financially motivated malicious software for OS X, Cluley said. Last week, the company spotted “OSX/Jahlav-A,” a Trojan downloader.

Jahlav is often planted on Web sites as a purported key generator that can be used to figure out valid product codes for hacked software. But if it is installed, a hacker has complete control over the Apple computer and can download other bad software to the machine to steal data, Cluley said.

Businesses that handle credit-card data using Apple computers may also be required to use antivirus software as part of recent security guidelines adopted by the payment card industry, Cluley said.

Additionally, Apple is now using Intel chips in its machines, which means some users may be using virtualization programs to also run Windows. Although the operating systems would run separately and can’t infect each other, it could increase the likelihood of an Apple user passing along Windows files that are infected to another person in the office, Cluley said.

Malicious software is “nowhere like as big of a problem as on Windows but it does exist,” Cluley said. “You can still get hit by it.”

Macworld.com staff contributed to this report.

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